This boolean specifies whether Generalized Brillouin Condition (GBC) is assumed to hold. The default is 'true'. This keyword is only valid if stdapprox=A'. The effect of setting this keyword to true is rather small -- hence it is not recommended to use this keyword.

ebc

This boolean specifies whether Extended Brillouin Condition (EBC) is assumed to hold. The default is 'true'. This keyword is only valid if stdapprox=A'. The effect of setting this keyword to true is rather small -- hence it is not recommended to use this keyword.

stdapprox

This gives a string that must take on one of the values below. The default is A'.

A

Use second order Mo/ller-Plesset perturbation theory with linear R12 terms in standard approximation A (MP2-R12/A). Only energies can be computed with the MP2-R12/A method.

A'

Use second order Mo/ller-Plesset perturbation theory with linear R12 terms in standard approximation A' (MP2-R12/A'). This will cause MP2-R12/A energies to be computed also. Only energies can be computed with the MP2-R12/A' method.

B

Use second order Mo/ller-Plesset perturbation theory with linear R12 terms in standard approximation B. This method is not implemented yet.

This specifies the auxiliary basis to be used for the resolution of the identity. Default is to use the same basis as for the orbital expansion.

vir_basis

This specifies the basis to be used for the virtual orbitals. Default is to use the same basis as for the orbital expansion.

include_mp1

This specifies whether to compute MP1 correction to the MP2 and MP2-R12 energies. This option only has effect if vir_basis is not the same as basis. MP1 correction is a perturbative estimate of the difference between the HF energy computed in vir_basis and basis. Usually, it is a very poor estimate -- therefore this keyword should be avoided by non-experts. Default is false.

abs_method

This string specifies whether the old ABS method, introduced by Klopper and Samson, or the new ABS variant, CABS, introduced by Valeev, should be used. Valid values are 'ABS' (Klopper and Samson), 'ABS+', 'CABS', and 'CABS+', where the '+' labels a method where the union of OBS and ABS is used to construct the RI basis. The default is 'ABS'. The default in 2.3.0 and later will be 'CABS+'.

lindep_tol

The tolerance used to detect linearly dependent basis functions in the RI basis set. The precise meaning depends on the orthogonalization method. The default value is 1e-8.

Store integrals in memory for single-pass situations and in a binary file on task 0's node using POSIX I/O for multipass situations. posix is usually less efficient than mpi for distributed parallel multipass runs since the I/O is performed by one task only. However, this method is guaranteed to work in all types of environments, hence mem-posix is the default.

posix

Store integrals in a binary file on task 0's node using POSIX I/O. This method is different from mem-posix in that it forces the integrals out to disk even if they could be stored in memory. posix should only be used for benchmarking and testing purposes.

mem-mpi

Store integrals in memory for single-pass situations and in a binary file using MPI-I/O for multipass situations. This method assumes the availability of MPI-I/O. mem-mpi is the preferred choice in distributed environments which have MPI-I/O available.

mpi

Store integrals in a binary file using MPI-I/O. This method is different from mem-mpi in that it forces the integrals out to disk even if they could be stored in memory. mpi should only be used for benchmarking and testing purposes.

mem

Store integrals in memory. Can only be used with single-pass transformations for MP2-R12/A and MP2-R12/A' methods. This method should only be used for testing purposes.

If r12ints is not specified, then mem-posix method will be used. If user wishes to use MPI-I/O, pending its availability, for higher parallel efficiency, r12ints should be explicitly set to mem-mpi.

r12ints_file

This specifies the prefix for the transformed MO integrals file if r12ints is set to posix, mpi, mem-posix or mem-mpi is used. Default is './<i>inputbasename</i>.r12ints', where inputbasename is the name of the input file without '.in'. If MPI-I/O is used then it is user's responsibility to ensure that the file resides on a file system that supports MPI-I/O.

twopdm_grid_aa

This optional keyword specifies a TwoBodyGrid object which to use for coordinates at which to compute alpha-alpha part of 2-PDM.

twopdm_grid_ab

This optional keyword specifies a TwoBodyGrid object which to use for coordinates at which to compute alpha-beta part of 2-PDM.